470 



from the point at the highest temperature the x"',^-curve graphed 

 by them in Fig. I, pi. 1, I.e., for nicker) has jnst the form wiiich 

 would be expected from Fig. 2*), 



§ 6. The po.s.sihiliti/ of the existence of ferroiiinynetic substances 

 vjithout CvY(m-poi7it. It was pointed ont in § 3a that on the assump- 

 tion of a zero-point energy for the molecular rotations the existence 

 must be considered possible of ferromagnetic substances (substances 

 with a molecular field), which do not show the specific ferromag- 

 netic properties. The condition for it was given in (14). Such a 

 substance will have to be looked for in the first instance among 

 those which have a large zero-point energy of rotation (a small 

 moment of inertia) and a small molecular magnetic moment, and 

 also a weak molecular field. 



From (7) follows, for states in which saturation has not yet 

 become appreciable, with (8), (10) and (11) for the susceptibility 



/— ' -^ Ur — 11 with 1' = — (oU) 



Ö 



In Fig. 3 are united the diiferent cases which are possible for 

 diff'erent values of the constant r, compared with Uy^- In this figure 

 for the different values of r -/"' has to be measured from the corre- 

 sponding horizontal line. 



If at constant molecular magnetic moment and constant zero-point 

 energy the molecular field increases from 0, we subsequently meet 

 with the following cases : 



v = t\. At sufficiently high temperatures / (2" -|- AJ =r const. 



1) Similar results they find for cobalt and iron. 



2) The observations by Weiss and FoËx concerning the susceptibility of 

 nickel above of the CuRiE-point can up to 870° G. be reasonably well represented 

 with the value 0(,:=2IOO of § 4 and with the magnetic moment of the gramme- 

 atom = 8552. This latter value differs from that derived in § 4 for the state 

 below the GuRiE-point. On account of provisional calculations il seems, however, 

 probable to me that for nickel the spontaneous magnetization beloiv the Curie- 

 point as iveli as the susceptibility in the excited ferromagnetic state above the 

 GvRiE point up to the temperature mentioned above, according to the measure- 

 ments by Bloch, Thesis Zurich (Techn. Hochsch.) 1912, presumably even up 

 to about 1200° G., can be represented with the same value of ©o a7id with the 

 same value of the magnetic moment per atom, and likewise with the same value 

 of the molecular field In a following paper 1 hope to communicate the results 

 of further calculations regarding this point. If these calculations lead to a confirm- 

 ation of that expectation, the significance of Weiss's theory of the molecular 

 field (completed by the assumption made in this communication regarding the 

 thermal equilibrium of these molecular rotations) will become even considerably 

 greater. 



